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Abstract

Nitrogen dioxide (NO₂) is a toxic pollutant that necessitates sensitive and reliable monitoring systems. Conventional gas sensors often lack adequate responsiveness and fast recovery under changing conditions and therefore create a need for semiconductors with enhanced performance, especially at high industrial temperatures (around 250 °C). The study therefore aims to synthesis and evaluate silver-doped cadmium telluride (Ag:CdTe) thin films as NO₂ gas sensors. Pure CdTe and Ag:CdTe with silver concentrations of 5, 10, and 15 wt% were prepared by a co-precipitation process. XRD verified cubic symmetry with a progressive fall in crystallite size (6.67 nm to 5.46 nm at 15 wt% Ag), which increases grain-boundary density and the availability of surface-active sites and improves sensitivity and response speed. Field-emission scanning electron microscopy revealed uniform spherical nanoparticles with diameters of 20 to 30 nm that form porous networks favourable for gas adsorption. Optical analysis by UV–Vis spectroscopy showed a direct bandgap decrease from 1.85 to 1.6 eV as silver content increased, which corresponds to a red shift of the absorption edge and reflects Ag-induced tail states and refined crystallite domains that facilitate carrier generation under NO₂. Gas sensing tests were performed under 5% NO₂ at 6 V between 25 and 250°C. Sensitivity increased with temperature and reached 81.6% for 0.15 Ag:CdTe films at 250°C. The Ag:CdTe sensor showed a response time of 5.3 s and a recovery time of 28 s. The findings demonstrate that Ag:CdTe films synthesized by co-precipitation present an efficient NO₂ gas sensors for controlled ambient monitoring.

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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